Bore Testing Device

ABSTRACT

A bore testing device for testing the inner surface of a bore in a workpiece is described. The bore testing device has a measuring head which defines an axial direction, and on which axial direction an optical system is situated which is in image transmission connection with a digital image sensor and a downstream evaluation apparatus. An apparatus for determining surface depth information from the output signals of the digital image sensor is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of German application No. DE 10 2014 114 304.3, filed Oct. 1, 2014, and this application claims priority of German application No. DE 10 2014 118 753.9, filed 18 Dec. 2014, and each of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a bore testing device for testing the inner surface of a bore in a workpiece.

BACKGROUND OF THE INVENTION

Bore testing devices of this type, also referred to as internal test sensors, are used to test the inner surfaces of bores, for bores, for example in the inspection of cylinder bores in crankcases. They are used for imaging the radial inner surface of the bore, and to check whether it meets predetermined requirements regarding surface quality.

Such devices are known from WO 2009/003692, DE 4416493 A1, DE 4320845 C1, and DE 3232904 C2, for example.

A bore testing device of this type for testing the inner surface of a bore in a workpiece is known from DE 10 2009 019 459 B4, having a measuring head which defines an axial direction, and on which an optical system with a panoramic view is situated which is in image transmission connection with a digital image sensor and a downstream evaluation apparatus. The testing device known from the cited publication also has an illumination arrangement for illuminating an imaging area of the inner surface which is detected by the optical system. The testing device known from the cited publication allows quick, accurate testing of inner surfaces of cavities, for example bores.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a bore testing device of the type for testing the inner surface of a bore in a workpiece which is improved with regard to the detection of surface defects in a bore in a workpiece.

This object is achieved by the invention set forth herein.

This object is achieved by the invention set forth herein which includes a testing device for testing the inner surface of a bore in a workpiece having a measuring head which defines an axial direction, and on which an optical system with a panoramic view is situated which is in image transmission connection with a digital image sensor and a downstream digital evaluation apparatus, as well as an apparatus for determining surface depth information from the output signals of the digital image sensor.

The invention provides an apparatus for determining surface depth information from the output signals of the digital image sensor. In this way, by means of the testing device according to the invention it is possible not only to image the inner surface of the cavity and test it by evaluating the resulting brightness image, but also to determine its topography. During the testing, if an anomaly is discovered on the inner surface in the evaluation of an image (camera image) recorded by the digital image sensor, by evaluating the output signal of the apparatus for determining surface depth information it may be concluded whether the detected anomaly is a depression in the surface, and therefore a manufacturing defect, or whether it is an elevation caused by soiling which may possibly be easy to remove.

In this manner, due to the additional surface depth information obtained, the test result obtained by means of a bore testing device according to the invention is much more meaningful than in testing devices which provide only imaging (brightness image) of the inner surface, without surface depth information. As a result, the detection of surface defects is improved. The apparatus for determining surface depth information from the output signals of the digital image sensor may have any suitable design, depending on the particular requirements. Thus, for example, it is possible to determine the topography of the surface to be examined based on shadow images, and thus obtain surface depth information, according to the known “shape from shading” method. However, any other measuring methods which operate in a contactless manner, in particular optical measuring methods such as confocal microscopy, which are suitable for measuring lengths or distances may be used.

In this regard, one advantageous further embodiment of the invention provides that the apparatus for determining surface depth information includes a white light interferometer, whose white light is coupleable or coupled into the beam path of the optical system for striking the inner surface to be examined. Such white light interferometers, whose design and function per se are generally known to those skilled in the art, may be used with high accuracy for determining surface depth information in the context of the invention. They are relatively simple in design and robust, and have a high level of measuring accuracy. In the context of the invention, the mode of action of a white light interferometer is that the white light of a light source is coupled into the beam path and split into a reference beam and a measuring beam by means of a beam splitter, the reference beam being reflected from a reference mirror, and the measuring beam being reflected from the surface of the measured object and scattered. The returning beams are relayed by the beam splitter to the digital image sensor, and form an interference signal for each individual pixel of the digital image sensor as a function of the topography of the inner surface. Each pixel of the digital image sensor scans this interference signal in the form of a white light correlogram when the length of the reference arm or the measuring arm of the white light interferometer is changed by means of a positioning unit. The interference signal of a pixel then has a maximum modulation when the optical wavelength of the light striking the pixel is exactly the same for the reference beam and for the measuring beam. The z value of a point on the inner surface to be tested, which is imaged on this pixel of the image sensor, thus corresponds to the z value of a positioning apparatus for positioning the reference mirror when the modulation of the correlogram is at a maximum. The surface depth information, and thus the topography, of the examined surface may then be ascertained by determining for each individual pixel the z value of the positioning apparatus for which the modulation of the output signal of this pixel is at a maximum. This embodiment thus allows surface depth information to be determined in a relatively simple manner.

To achieve a design, e.g., a setup, in a simple and cost-effective manner in the above-mentioned embodiment, one advantageous further embodiment of the invention provides that a positioning apparatus is associated with a reference mirror of the white light interferometer, the positioning apparatus being controllable by a control apparatus which is in data transmission connection with the evaluation apparatus in such a way that the evaluation apparatus assigns associated output signals of the digital image sensor to different positions of the reference mirror. The modulation of the interference signal of a pixel is thus changed by positioning the reference mirror with the aid of the positioning apparatus. A high level of measuring accuracy may thus be achieved by using a positioning apparatus having high positioning accuracy.

In other respects, the design and function of a white light interferometer are generally known to those skilled in the art, and therefore are not explained here in greater detail.

By the use according to the invention of an optical system (imaging optics) with a panoramic view, the inner surface of the cavity is imaged on the digital image sensor along a circumferential lateral surface line. In order to examine different axial areas of the cavity, one advantageous further embodiment of the invention provides that an advancing apparatus for advancing the measuring head in the axial direction in a stepwise or continuous manner is associated with the measuring head.

Another further embodiment of the invention provides that at least the measuring head, preferably the measuring head together with an illumination arrangement for illuminating the inner surface, is designed as an endoscope which is insertable into the bore to be tested.

In the context of the invention, a bore is understood to mean any rotationally symmetrical or substantially rotationally symmetrical recess in a workpiece, regardless of how the recess has been introduced into the workpiece, for example by drilling or by means of some other machining process, or by molding or the like. In the context of the invention, a substantially rotationally symmetrical recess is understood to mean that the basic shape of the recess is rotationally symmetrical, but may contain grooves or the like, for example. Within the meaning of the invention, a rotationally symmetrical recess is of course understood to mean a recess whose basic shape deviates from rotational symmetry due to anomalies.

The invention is explained in greater detail below with reference to the appended drawing, in which one embodiment of a bore testing device according to the invention is illustrated in a highly schematic manner. All features, alone or in any arbitrary combination, which are described, illustrated in the drawing, and claimed in the patent claims constitute the subject matter of the present invention, regardless of their recapitulation in the patent claims or their back-reference.

Relative terms such as left, right, up, and down are for convenience only and are not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE is a schematic side view of an embodiment of a bore testing device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The single FIGURE of the drawing illustrates in a highly schematic manner a side view of one embodiment of a bore testing device 2 according to the invention for testing the inner surface 4 of a bore 6 in a workpiece 8 (bore inspection device), having a measuring head 10 which defines an axial direction. The corresponding axis is symbolized in the figure by a dash-dotted line 12, and coincides with the optical axis of an optical system 14 (imaging optics) with a panoramic view of 360°, situated on the measuring head 10. The optical system 14 is in image transmission connection with a digital image sensor 16 and a downstream digital evaluation apparatus. The evaluation apparatus has been omitted in the drawing for reasons of simplicity.

By means of the optical system 14 with a panoramic view, the inner surface 4 of the bore 6 is imaged on the digital image sensor 16 along a circumferential lateral surface line 16 in the peripheral direction. The resulting output signal of the digital image sensor 16 is examined for anomalies or defects of the surface 4 in the downstream digital evaluation apparatus. The basic mode of functioning of such a bore testing device is generally known to those skilled in the art, and therefore is not explained here in greater detail. In this regard, reference is made in particular to DE 10 2009 019 459 B4.

To illuminate the inner surface 4, an additional illumination arrangement may be provided, depending on the particular circumstances; this additional illumination arrangement has been omitted in the drawing for reasons of simplicity.

To position the measuring head 10 relative to the inner wall 4 in the axial direction, an advancing apparatus (symbolized by a double arrow 18 in the drawing) for advancing the measuring head 10 in a stepwise or continuous manner in the direction of the axis 12 is associated with the measuring head 10. According to the invention, the bore testing device 2 has an apparatus for determining surface depth information from the output signals of the digital image sensor 16, in the illustrated embodiment this apparatus for determining surface depth information includes a white light interferometer 20 having a broadband light source 22.

The beam 24 of the light source 22 is split into a measuring beam 28 and a reference beam 30 by means of a beam splitter mirror 26. The measuring beam 28 is coupled into the beam path of the optical system 14 and strikes the inner surface 4. The reference beam 30 is deflected onto a reference mirror 32, which in the illustrated embodiment takes place via a deflection mirror 34, which, however, is not necessary for the basic functioning of the white light interferometer, and is provided in the illustrated embodiment solely for structural reasons.

A positioning apparatus, which is symbolized by a double arrow 36 in the drawing and is used for changing the length of the reference beam by linear positioning of the reference mirror 32, is associated with the reference mirror 32. The reference beam reflected from the reference mirror 32 is deflected onto the image sensor 16 via the beam splitter 26. The measuring beam 24 strikes the inner surface 4, is reflected by same, and likewise reaches the image sensor 16 via the optical system 14.

An interference thus results on each pixel of the image sensor 16 when the optical wavelengths of the measuring beam 24 and of the reference beam 30 are virtually identical. Each pixel of the image sensor 16 scans a white light correlogram (interference signal) when the position of the reference mirror 32, and thus the optical wavelength of the reference arm of the white light interferometer 20, is changed by means of the positioning unit 36. In other respects, the functioning of a white light interferometer is generally known to those skilled in the art, and therefore is not explained here in greater detail. In the test position of the measuring head 10, its axial device corresponds to the axial direction of the bore 6. The bore testing device 2 according to the invention functions as follows:

The measuring head 10, which in this embodiment is designed, i.e., configured, as an endoscope, is inserted into the bore 6 to be examined, the optical system 14 detecting an image of the inner wall 4 of the bore 6 along a circumferential lateral surface line and imaging same on the image sensor 16. By evaluating the recorded brightness image, i.e., the output signals of the image sensor 16, it may be concluded, using known methods of image processing and pattern recognition, whether an anomaly or defect is present on the inner wall 14.

The measuring beam 24 and the reference beam 30 of the white light interferometer 20 result in simultaneous interference on each pixel of the image sensor 16; by positioning the reference mirror 32, for each pixel of the image sensor 16 it may be determined when the modulation is at a maximum. When the modulation of the correlogram is at a maximum, the associated positioning path of the positioning unit 36 corresponds to the maximum value of the point on the inner surface 4 which is imaged on this pixel. Surface depth information may be obtained in this way, so that the topography of the inner surface 4 may thus be determined. Based on the surface depth information, it may be concluded whether a detected anomaly is a depression in the surface which forms a surface defect, or is an elevation on the surface caused by soiling, for example.

The testing device according to the invention is thus improved with regard to the detection of surface defects in a cavity in a workpiece.

Depending on the particular requirements, the surface depth information may be determined for each pixel of the recorded brightness image, so that the topography of the inner surface of the bore may thus be determined over the entire surface. However, it is also possible to determine the surface depth information, and thus the topography of the inner surface, not over the entire surface, but instead at individual surface locations as needed. In this regard it is possible and meaningful in particular to determine the surface depth information only at the surface locations at which an anomaly has been identified, since only those surface locations at which an anomaly exists are important for the test result. Thus, in principle there is no need for determining the surface depth information at surface locations without anomalies.

By means of the bore testing device according to the invention, when an anomaly is detected it may thus be concluded whether this is, for example, a depression resulting from a surface defect, or an elevation caused by soiling which may possibly be eliminated by removing the soiling. Thus, due to the surface depth information which is available using the bore testing device according to the invention, the test result is much more meaningful than in conventional devices.

While this invention has been described as having a preferred design, it is understood that it is capable of further modifications, and uses and/or adaptations of the invention and following in general the principle of the invention and including such departures from the present disclosure as come within the known or customary practice in the art to which the invention pertains, and as may be applied to the central features hereinbefore set forth, and fall within the scope of the invention. 

What is claimed is:
 1. A testing device for testing the inner surface of a bore in a workpiece, comprising: a) a measuring head which defines an axial direction, and on which an optical system with a panoramic view is situated which is in image transmission connection with a digital image sensor and a downstream digital evaluation apparatus; and b) an apparatus for determining surface depth information from the output signals of the digital image sensor.
 2. Testing device according to claim 1, wherein: a) the apparatus for determining surface depth information includes a white light interferometer having a light source whose light is one of coupleable and coupled into the beam path of the optical system for striking the inner surface.
 3. Testing device according to claim 2, wherein: a) a positioning apparatus is associated with a reference mirror of the white light interferometer, the positioning apparatus being controllable by a control apparatus which is in data transmission connection with the evaluation apparatus in such a way that the evaluation apparatus assigns the associated output signals of the digital image sensor to different positions of the reference mirror.
 4. Testing device according to claim 1, wherein: a) an advancing apparatus for advancing the measuring head in the axial direction in one of a stepwise and a continuous manner is associated with the measuring head.
 5. Testing device according to claim 1, wherein: a) one of: i) the measuring head; and, ii) the measuring head together with an illumination arrangement is configured as an endoscope which is insertable into the cavity to be tested. 